The use of protective gas-inflated bags to cushion vehicle occupants in crash situations is now widely known and well documented. In earlier systems of this type, a quantity of compressed, stored gas was employed to inflate a crash bag which, when inflated, was positioned between the occupant and the windshield, steering wheel and dashboard of the vehicle. The compressed gas was released by rapid impact responsive to actuators or sensors which sense a rapid change in velocity of the vehicle as in an accident situation.
Because of the bulk of this apparatus, its generally slow reaction time and its maintenance difficulties, stored gas systems have largely been superseded by systems that utilize a gas generated by a chemical gas generating substance or composition. These systems involve the use of an ignitable propellant system for inflating the air cushion, wherein the inflating gas is generated by the exothermic reaction of the reactants forming the propellant composition. The bags used in a restraint system of this type must be inflated to a sufficient degree in a very short time span, generally on the order of tens of milliseconds, to accomplish their purpose. In addition, the gas should meet several rather stringent requirements. It should be nontoxic and non-noxious. The temperature of the gas as generated should be low enough so as not to burn the bag, undermine its mechanical strength, or burn the passengers in the vehicle in the event the bag ruptures.
The industry has been striving to develop a gas generating composition which combines the essential features of short induction period, a burn rate which is rapid but without explosive effects, a high bulk density so that only a small amount of the composition is required to produce a large amount of gas and the production of only nontoxic and non-noxious gases.